linux-kernel - Re: include/net/sock.h:2100:16: sparse: sparse: cast to non-scalar

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Message-ID: <20260113152705.GX830755@noisy.programming.kicks-ass.net>
Date: Tue, 13 Jan 2026 16:27:05 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: kernel test robot <lkp@...el.com>, Eric Dumazet <edumazet@...gle.com>,
	oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
	Jakub Kicinski <kuba@...nel.org>,
	Maciej Żenczykowski <maze@...gle.com>,
	Will Deacon <will@...nel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: include/net/sock.h:2100:16: sparse: sparse: cast to non-scalar

On Mon, Jan 12, 2026 at 07:30:19PM +0000, Al Viro wrote:

> Sure, but what does that have to do with the final cast in there?  Note
> that generic __READ_ONCE() ends up with __unqual_scalar_typeof(x) for the
> type of result and it seems to be working fine.
> 
> Why would the same type of result be a problem for alpha?  Sure, we need
> a barrier there, so it can't be literal copy of generic __READ_ONCE(),
> but what's the problem with using
> 
> #define __READ_ONCE(x)							\
> ({									\
> 	__unqual_scalar_typeof(x) __x =					\
>  		(*(volatile typeof(__x) *)(&(x)));			\
> 	mb();								\
> 	__x;								\
> })
> 
> there?  What could possibly need those qualifiers added back to the result?
> It is, after all, an r-value, so...

Yeah, I'm not sure about the final cast, that was probably trying to add
'const' back.